Biomedical electrodes are used for diagnostic and therapeutic purposes including electrocardiographic monitoring and diagnosis, electrosurgery, iontophoretic (electrically enhanced) transdermal delivery of drugs, and defibrillation. In their most basic form, these electrodes have a conductive medium contacting mammalian skin and a means for electrical communication interacting between the conductive medium and electrical diagnostic, therapeutic, or electrosurgical equipment.
The conductive medium used in these electrodes is generally an ionically conductive adhesive or gel. A conductive adhesive composition which both serves to adhere a biomedical electrode to skin and to establish an electrical connection between skin and an electrical medical apparatus should desirably have multiple characteristics which are difficult to achieve in one composition. At minimum, the composition should have the characteristics of a good medical adhesive and those of a good ionic conductor. A good medical pressure-sensitive adhesive needs to be dermally non-irritating, compliant and tacky enough so as to wet onto skin and adhere, and sufficiently cohesive both to resist shear and peel forces and to pull away from skin without leaving a residue. To optimize electrical performance, low impedance at the interface of the composition and the skin is desirable.
It is known that ionically conductive adhesives can be compounded from a polar polymeric network which is plasticized with a humectant material such as glycerin or poly(ethylene glycol). Water, a salt, or a pharmaceutical can also be included depending on the application. Generally a relatively thick layer of adhesive or gel is used (10 to 100 mil (0.25 to 2.5 mm) or greater).
Much work has been done in recent years to optimize conductive adhesives for biomedical applications, to achieve better properties in one area without having to compromise excessively in another. One area that has not had as much development is the preparation of conductive adhesives that are melt processable after the polymeric material has been formed for use in the manufacture of a biomedical electrode. The available materials are viscous, cohesive, and non-water soluble. Once placed by polymerization onto a backing material, they cannot be practically reprocessed or recycled. Any adhesive that is placed on material, i.e., the "weed" which is cut away during the automated die cutting of bioelectrodes, must now be discarded as waste.
In addition, known processing methods involve polymerization on the substrate or coating from a carrier solvent (organic or water). These processes are typically slow and can involve difficult drying steps because of the thickness of the electrode material.